Fluid handling structure for use in absorbent articles

ABSTRACT

Fibers having intra-fiber capillary channels are used in conjunction with topsheet materials in absorbent articles such as diapers, bandages and, especially, sanitary napkins. In-use, the capillary channel fibers draw fluid away from the topsheet to provide a clean, dry appearance.

This is a continuation of application Ser. No. 07/734,392, filed on Jul.23, 1991, now abandoned.

TECHNICAL FIELD

The present invention relates to absorbent articles, especiallycatamenial articles such as sanitary napkins. Such articles areespecially adapted for absorbing various body fluids, especially menses,while providing comfort and fit to the wearer.

BACKGROUND OF THE INVENTION

A wide variety of structures for disposable absorbent articles tocollect body fluids are known in the art. Commercial absorbent articlesinclude diapers, adult incontinence products, catamenials and bandages.Disposable products of this type comprise some functional members forreceiving, absorbing and retaining fluids. Generally, such absorbentarticles contain a core of absorbent materials mainly comprising fibrouscellulose. Typically, such articles include a fluid-permeable topsheet,an absorbent core and a fluid-impermeable backsheet.

In the case of catamenial pads, women have come to expect a high levelof performance in terms of comfort and fit, retention of fluid, andminimal staining. Above all, leakage of fluid from the pad ontoundergarments is regarded as totally unacceptable.

Improving the performance of sanitary napkins continues to be aformidable undertaking, although a number of improvements have been madein both their materials and structures. However, eliminating leakage,particularly along the inside of the thighs, without compromising fitand comfort, has not met the desired needs of the consumer.

Leakage from sanitary napkins is generally attributed to a highconcentration of fluid at the point where the menses exits the body andimmediately contacts the surface of the napkin. At this point ofdeposit, the napkin's absorbent material quickly becomessuper-saturated. The blood migrates radially from this point and leaksfrom the sides nearest the wearer's legs. This often results in thesmearing of blood on the body and soiling of the undergarments. Attemptsto eliminate leakage include: construction of a densified edge to holdthe fluid back (U.S. Pat. No. 4,820,295, Chapas et al, issued Apr. 11,1989); barrier sheets surrounding the article (U.S. Pat. No. 4,666,439,Williams et al, issued May 19, 1987); and "winged" side edges which wraparound the panties (U.S. Pat. No. 4,701,177, Ellis et al, issued Oct.10, 1987, incorporated herein by reference).

Unfortunately, overdensifying sections of the sanitary napkins detractsfrom comfort, in-use. Some users are not attracted to the "winged"product, and others are not satisfied with the barrier product. However,since a large part of most absorbent articles remains relatively dry andnot utilized, it has now been determined that providing a means todirect fluid from the point of deposit to the areas of the article notfully utilized will avoid super-saturation and considerably reduce oreliminate leakage.

Apart from undergarment soiling, the user of modern sanitary napkins,and the like, has come to expect that the surface of such articles willprovide a cleaner, more sanitary and drier aspect than common cloth ornonwoven materials have historically provided. Thus, modern sanitarynapkins, diapers and incontinence devices are typically provided withtopsheets that are designed to move fluids rapidly through saidtopsheets and into an underlying absorbent core for storage. As can beenvisaged, the more rapid and thorough this movement, the drier andcleaner the surface of the article.

Stated succinctly, the present invention not only provides the desired,directional movement of fluids noted above, which allows improved use ofthe overall absorbent capacity of the article and less side-leakage, butalso provides means to draw fluids through the topsheet, therebyenhancing the desired dry, sanitary benefits, in-use.

Furthermore, the articles which employ the technology embodied in thepresent invention are more comfortable and better fitting than articleswhich rely, for example, on highly dense absorbent core regions toachieve fluid movement. Stated otherwise, the technology herein achievesthe fluid directionality and handling characteristics available fromdense, but uncomfortable, cores in a soft, pliable, low-density andcomfortable pad.

It is, therefore, an object of the present invention to providedisposable absorbent articles having improved fluid absorption andretention. It is a further object herein to provide such articles withimproved fluid transport away from the skin. It is a particular objectherein to provide sanitary napkins and pantiliners with attributesincluding, but not limited to, improved softness and flexibility,improved fit and improved stain reduction.

These advantages are obtained herein, as will be seen from the followingdisclosure.

BACKGROUND ART

Disposable articles used to retain human body fluids and waste are wellknown in the art. U.S. Pat. No. 3,860,003, Buell, issued Jan. 14, 1975,and U.S. Pat. No. 3,670,731, Harmon, issued Jun. 20,1972, disclosedisposable diapers and their manufacture. The diapers disclosed thereincontain a significant amount of cellulose material to absorb and retainchildren's urine and feces.

The technology used in diapers is also used in the field of catamenialproducts such as pads, sanitary napkins, and pantiliners. Althoughsimilar objectives are sought among all the aforementioned products,catamenial products do require some specialized needs for active womenas opposed to, diapers for a baby. Minimizing size, improving fit andcomfort, and stain inhibition have been the motivation for many of thedevelopments disclosed in the art.

Early patents on disposable catamenials include U.S. Pat. No. 2,662,527,Jacks, Dec. 15, 1953, which discloses a sanitary pad characterized inthat it has a portion which at least partially resides outside andwithin the lips of the wearer's labia. Cellulosic-type fibers are usedas the absorbent materials for such pads.

Since Jacks, catamenial pads have been separated into at least twogeneralized classes. These classes are broken down as pads which havethe capability to absorb large or heavy flows of menses and those onlyintended for small or light flows.

Catamenial articles disclosed in U.S. Pat. No. 4,654,040, Luceri, Mar.31, 1987, are provided with a "tuck" to produce a body contouredproduct. The pads disclosed therein can be cellulosic as well asmixtures of cellulosic and polyester/polyethylene conjugate fibers.

The second class of pads, traditionally used for light flows, areexemplified in U.S. Pat. No. 4,701,177, Ellis et al. The pads disclosedtherein have a high bulk density, meaning that the fibrous material istightly compressed together. Normally, these pads are no more than about1/2 inch thick.

Thinner pads have become increasingly popular. U.S. Pat. No. 4,950,264,Osborn, Aug. 21, 1990, discloses a thin-style sanitary napkin having abody surface and a garment surface wherein the absorbent core is madevery flexible by including polymer gelling agents with the fibrousmaterial. These pads have the capacity to handle medium to highmenstrual flows.

Polymer gelling agents have been incorporated in absorbent articles inpart to achieve a thin profile without sacrificing flexibility; see U.S.Pat. No. 4,662,876, Wiegner, issued May 5, 1987; U.S. Pat. No.4,865,596, Weisman et al, issued Sep. 12, 1989; and U.S. Pat. No.4,923,454, Seymour et al, issued May 8, 1990.

One of the keys to the present invention is the use of materials whichpromote fluid directionality. Various methods to achieve this includeformation of a channel patterns to direct fluids; see U.S. Pat. No.4,781,710, Megison et al, issued Nov. 1, 1988; integration of a webstructure in the article; see U.S. Pat. No. 4,637,819, Ouellette et al,issued Jan. 20, 1987, and chemical modification of cellulose fibers; seeU.S. Pat. No. 4,256,111, Lassen, Mar. 17, 1981.

EPO Application 391,814, Phillips et al, published Oct. 10, 1990,discloses capillary channel fibers which spontaneously transport liquidsand are suitable for use in absorbent articles, wherein the fibers arelocated near the center of the article. By using the fibers in thismatter, fluid can be transported to a larger surface area on thearticle.

U.S. Pat. No. 4,723,954, Pieniak, Feb. 9, 1988, relates to an absorbentarticles comprising a nonwoven fabric facing sheet and an absorbentbatt. Some of the fibers of the batt extend into and are integral withthe facing fabric. The extended fibers assertedly promote wicking ofliquid through the facing and into the batt and stabilize the batt.

U.S. Pat. No. 4,798,603, Meyer et al, Jan. 17, 1989, relates toabsorbent articles comprising a hydrophilic absorbent body, a liquidpermeable topsheet, a liquid permeable transport layer between saidtopsheet and said absorbent body, wherein the effective average poresize in said transport layer is smaller than the pore size in thetopsheet, and wherein the transport layer is less hydrophilic than theabsorbent. The transport layer is configured so that it is capable ofattaining a substantially intimate contact with the topsheet and theabsorbent body, which is said to be useful for providing an effectivefluid communication from the topsheet to the transport layer and fromthe transport layer to the absorbent body. The transport layer is saidto be able to allow a rapid spread of liquid sideways along its laterallength and width dimensions to expose a larger surface area of theabsorbent body to liquid.

U.S. Pat. No. 4,973,325, Sherrod et al, Nov. 27, 1990, relates to anabsorbent article having a pair of absorbents positioned adjacent toeach other. A fluid impermeable baffle and fluid transfer member aresaid to facilitate the movement of body fluids from the cover downwardand outward to distant areas of the absorbents.

EPO Application 397,110, Latimer et al, filed Aug. 5, 1990 relates to anabsorbent article comprising a surge management portion of a selectedbasis weight which is said to rapidly uptake and temporarily hold atleast three successive surges of fluids.

French Patent 955,625, Paul Chevalier, "Improvements in SpinningArtificial Fiber", published Jan. 16, 1950, discloses fibers ofsynthetic origin with allegedly improved capillarity. Chevalierdisclosed the primary use of these fibers as absorbing material formaking towels, handkerchiefs, bath mats and the like. The fibers aresaid to have continuous or discontinuous grooves positioned in thelongitudinal direction, i.e., parallel to the fiber axis. The fibers mayhave a central nucleus from which radiate radial leaves. This patentalso discloses a process for making the fibers involving a firstspinneret for forming the fibers into the desired shape and a secondspinneret in direct communication with the first, separated from thefirst by an insulating plate, for cooling the fiber. The secondspinneret is in contact with a cooling element.

U.S. Pat. No. 3,121,040, Gilbert Shaw, "Unorientated PolyolefinFilaments", issued Feb. 11, 1964, discloses a variety of plasticfilaments, and a process for making them, which assertedly exhibit goodrecovery after deformation, and resist orientation (i.e., matting) uponuse in such applications as paint brushes. These objects are said to beachieved by preparing fibers having cross-sections consisting ofinterconnected webs with web length, web thickness, and radius ofparticular, specified requirements.

U.S. Pat. No. 4,054,709, M. N. Belitsin, et al, "Man-Made Fibre, Yarnand Textile Produced Therefrom", issued Oct. 18, 1977, discloses fibersof polycaproamide and polyethylene terephthalate displaying a crosssectional shape formed of at least two elements formed of intersectingrays which define open capillary channels and a bridge interconnectingparticular rays of the elements. The rays intersect at angles of from10° to 70° to form the capillary channels. The fibers are said toexhibit an appearance and moisture conductivity and absorptionapproaching natural silk. See also U.S. Pat. No. 4,179,259, Belitsin,which includes some curling disclosure.

U.S. Pat. No. 4,381,325, Yutaka Masuda, et al, "Liquid RetainingSynthetic Fiber, Process for Producing the Same, and Products", issuedApr. 26, 1983 discloses a liquid-retaining tapered portion. The fibersdisclosed include embodiments having a plurality of channels runningalong the axial length of the fibers.

European Patent Application 88306987.4, publication number 0,301,874,published Feb. 1, 1989, Andrew G. Wilkes and Alan J. Bartholomew,"Cellulosic Fibre", discloses viscous filaments having multi-limbedcross-section, e.g., Y-, X-, H-, and T- shapes which are said to beuseful for absorbent products and woven and nonwoven fabrics.

U.S. Pat. No. 4,286,005, Richard M. Berger, "Ink Reservoir Element forUse in a Marking Instrument, and Method and Apparatus for ProducingSame", issued Aug. 25, 1981, discloses an ink reservoir element formedfrom a coherent sheet of flexible thermoplastic fibrous material orfoam-attenuated extruded polyester fabric, which has been uniformlyembossed with a series of parallel grooves. The embossed sheet iscompacted and bonded into a dimensionally stable body whose longitudinalaxis extends parallel to the embossed grooves.

U.S. Pat. No. 4,623,329, James L. Drobish, et al, "Drainage and InfusionCatheters Having a Capillary Sleeve Forming a Reservoir for a FluidAntimicrobial Agent", issued Nov. 18, 1986, discloses catheter tubesprovided at the inner surfaces with longitudinally extending capillarychannels or grooves. The grooves preferably exhibit a favorable surfacecontact angle for the particular fluid to be dispensed. Surfacetreatments to alter the surface contact angle can be applied.

Japanese Patent Application 151617-1979, published Nov. 29, 1979, TeijinKK, "Synthetic Fibers", discloses various modified-profile syntheticfibers, especially of polyester or polyamide, having a cross-sectionshape characterized by fine pores running in the axial direction havingdiameter of 0.01 microns to 5 microns and a total cross-sectional areaof the pores of 0.016 to 50% of the total cross-sectional area of thefibers. The fibers can have additives for increasing water absorptionproperties.

U.S. Pat. Nos. 4,842,792, issued Jun. 27, 1989, and 4,954,398, Sep. 4,1990, both to Bagrodia et al disclose the process for making and thepolyester fibers made from such a process wherein the fibers have atleast one grove wherein the surface of the groove is rougher than thesurface outside the groove. Such fibers are used to improve cover,softness, and wetting characteristics of fabrics or yarn made from suchfibers.

U.S. Pat. No. 4,868,031, Modrak et al , issued Sep. 19, 1989, disclosessoft water-permeable polyolefins nonwovens having opaquecharacteristics. This invention utilizes fibers having characteristicshapes to improve the opacity and stain-masking properties of coverstocks. The fibers that are disclosed for use in this invention includethose having cross-sectional shapes selected from the group consistingof a diamond, a delta, "Y", "X", "O", an oval, a square, a rectangle,and the like.

SUMMARY OF THE INVENTION

The present invention encompasses structures suitable for use inabsorbent articles such as diapers, catamenials, adult sanitaryproducts, bandages, and the like, which are typically designed to bedisposed of after a single use. The structures herein are especiallyuseful in catamenials such as sanitary napkins and pantiliners.

One fluid receiving and fluid transporting structure of this inventionwhich is suitable for use in an absorbent article, comprises:

(a) a fluid permeable nonfibrous formed-film topsheet having afluid-receiving front face and a back face, said topsheet havingmultiple openings communicating between said front face and said backface for passage of fluid through said topsheet; and

(b) a layer comprising multiple fibers having external intrafibercapillary channels underlying the back face of said topsheet and influid-transporting contact therewith; wherein, the width of saidopenings in said topsheet (a) is, on average, larger than the width ofthe intrafiber capillary channels in said layer (b).

In such structures, the contact between the topsheet and the layer ofcapillary channel fibers can be maintained by tensional forces betweensaid topsheet and said layer. Preferably, the contact between thetopsheet and the layer of capillary channel fibers is maintained bybonding means, most preferably by means of adhesive laid-down in aspiral or multiple spiral pattern.

Preferred structures are those wherein the capillary channel fibers aresubstantially curled, and most preferably are substantially curled andare positioned such that their channels lie substantially in the machinedirection.

Highly preferred structures herein are those wherein the capillarychannel fibers are substantially curled, and wherein a portion of thefibers partially protrudes into, or into and through, said formed-filmtopsheet.

The invention also encompasses a sanitary napkin, pantiliner, diaper,adult incontinence garment, bandage, or the like, comprising thestructure of Claim 1, and additionally comprising: (c) afluid-impermeable backsheet underlying said capillary channel fiberlayer (b) .When said capillary channel fiber layer (b) has anintra-fiber retention capacity for menses of at least about 2 cm³ pergram, there may be no need for the inclusion of additional absorbentmaterial into the article, e.g., in a pantiliner or sanitary napkin forlight menstrual flow.

The invention also encompasses a fluid receiving and fluid transportingstructure suitable for use in an absorbent article, comprising:

(a) a fluid permeable fibrous topsheet having a fluid-receiving frontface and a back face, said topsheet having multiple interfiber openingscommunicating between said front face and said back face for passage offluid through said topsheet;

(b) a layer comprising multiple fibers having external capillary channelunderlying the back face of said topsheet and in fluid-transportingcontact therewith; wherein, the interfiber spacings which comprise theopenings in said topsheet (a) are, on average, larger than the width ofthe intrafiber capillary channels in said layer (b).

The capillary channel fibers are preferably spontaneously wettable andare, typically, hydrophilic or hydrophilized.

Again, such structures will typically have the contact between thetopsheet and the layer of capillary channel fibers maintained bytensional forces between said topsheet and said layer, or, preferably,by bonding means as noted above. As noted, the capillary channel fibersare preferably substantially curled, and, most preferably, arepositioned such that their channels lie substantially in the machinedirection. Also as noted above, the capillary channel fibers arepreferably curled and a portion of the fibers preferably partiallyprotrudes into said fibrous topsheet. Various absorbent structures usingthe fibrous topsheet are thus provided, with the addition of afluid-impermeable backsheet underlying said capillary channel fiberlayer (b).

While the capillary channel fibers employed herein are typicallynoncellulosic and are conveniently of the polyester type, it will beappreciated that other types of fiber-forming polymers can be used intheir preparation. For example, polyalkenes, polyamides, polylactates,poly-dioxanones, and the like, can be used. Since the objective hereinis to have the capillary channel fibers direct, rather than absorb, bodyfluids, it is preferred that the fibers have minimal, or substantially,no, fluid-imbibing (i.e., water-based body fluids) properties. It willbe readily appreciated that, if the fibers themselves absorb fluids andswell, the capillary channels could be choked-off. Thus, cellulosederivatives, for example cellulose propionate, cellulose acetate, andthe like, also may be used, if desired, only with due regard for theforegoing considerations.

In a preferred embodiment, the structures herein are prepared in suchfashion that at least some of the capillary channel fibers protrude intoat least some (preferably, at least about 30%, more preferably, at leastabout 50%) of the openings in that portion of the topsheet whichoverlays the capillary channel fibers. In yet another mode, at leastsome of the capillary channel fibers can be needle-punched or otherwisecaused to protrude through at least some (preferably at least about 30%,more preferably, at least about 50%) of the openings in that portion ofthe topsheet which overlays the capillary channel fibers. In this latterinstance, the capillary channel fibers will typically protrude throughthe topsheet for distances of from about 0.1 mm to about 3 cm. Thisprovides for very active uptake of fluid through the topsheet and intothe internal region of the fluid-handling structure.

All percentages, ratios and proportions herein are by weight, unlessotherwise specified. The patents and applications mentioned in thisdocument are incorporated herein by reference.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a direct view of an extrusion die (1) having an orifice (2) ofa design suitable for making symmetrical "H" shaped capillary channelfibers having a planar base and capillary channels extendingsymmetrically from opposite sides of said base.

FIG. 2 is a cross-sectional view of a symmetrical "H" shaped capillarychannel fiber (3) with planar base (4), width-between-walls (5) anddepth-of-walls (6) made by the extruding a polymer through the die ofFIG. 1.

FIG. 3 is a direct view of an alternate extrusion die (7) having anorifice (8) design suitable for making "multiple H" shaped capillaryfibers having a planar base and multiple capillary channels extendingsymmetrically from opposite sides of said base and all optionally havingapproximately the same channels widths and heights.

FIG. 4 is a cross-sectional view of a capillary channel fiber made bythe extruding a polymer through the die of FIG. 3.

FIG. 5 is a cross-sectional view of a multiple "U"-shaped fiber.

FIG. 6A is a cross-sectional view of an H-shaped capillary channel fiberin a partially collapsed state. While not optimal, such fibers can beused herein.

FIG. 6B is a cross-sectional view of an expanded capillary channelfiber. Such fibers can be used herein.

FIG. 6C is a cross-sectional view of a wholly collapsed capillarychannel fiber. Such fibers are not used herein.

It is to be understood that FIGS. 1-6C are only for purposes ofillustration and are not drawn to scale, inasmuch as the thickness ofthe walls and planar base of the capillary channel fibers can be, andpreferably are, relatively much thinner than the width-between-walls.The thinner the walls and base, the more pliable the fiber, and thehigher the fluid capacity.

FIG. 7 is a cross-sectional view of a catamenial pad with the view beingalong the longitudinal axis of the pad. The cross-section showsfluid-permeable topsheet (9), a layer or "secondary topsheet" (10)comprising the capillary channel fibers herein, a fluid retaining core(11), and a fluid impervious backsheet (12).

FIG. 8A is a cutaway perspective view of a catamenial pad having a fluidpermeable topsheet (13), a fluid distributing capillary channel fiberlayer, i.e., as a "secondary topsheet" (14) substantially covering afluid retaining core (15) and a fluid impervious backsheet (16).

FIG. 8B is a cutaway perspective view of a catamenial pad having a fluidpermeable topsheet (17) a capillary channel fiber layer (18) said layernot covering the peripheral edge (19) and terminating about one inchfrom the end of absorbent core (20). Backsheet (21) is also shown.

FIG. 9 is a perspective view of a catamenial pad wherein the contactbetween the various layers is achieved by multiple compression lines(22).

FIG. 10 illustrates the underside of a porous topsheet (23) and thepreferred multispiral pattern of glue lines (24) used to affix thetopsheet to the layer of capillary channel fibers. The machine directiondimension (25) of the pattern used on a typical catamenial is about 7inches and the cross-direction dimension (26) is about 2 inches.

FIG. 11 shows the underside of a porous topsheet (27) and a pattern ofadhesive spots (28) having machine direction dimension (29) andcross-direction dimension (30).

FIG. 12 is a photomicrograph of a section taken of formed film topsheet(31) and the layer of capillary channel fiber (32). The close contactbetween the capillary channel fibers and the topsheet is shown by theprotrusion of capillary channel fibers (33) into pores (34) in thetopsheet.

FIG. 13 is an exploded view of the sanitary napkin of Example I, withtopsheet (35), a layer of CCF SW194 capillary channel fibers (36), aswatch of CCF SW173 capillary channel fibers (37) underlying layer (36),a creped paper towel (BOUNTY™) layer (38), a wet-laid fibrous absorbentcore (39) with slitted (40) and unslitted (41) areas and containingabsorbent gelling material, backsheet (42) polyethylene end guards (43),optional release paper (44), and showing the relative placement of eightstrips of panty fastening adhesive (45). In use, the panty fasteningadhesive strips remain on the outer side of backsheet (42) when releasepaper (44) is removed from the article.

DETAILED DESCRIPTION OF THE INVENTION

As a point of reference, attention is drawn to FIG. 10. In accord withcommon practice, the long (or "x") axis is referred to as the "machinedirection", inasmuch as, during manufacture the articles pass throughthe machine in the direction of this axis. The short (or "y") axis isreferred to as the "cross direction", since it is the direction acrossthe width of the article. The "z" direction is the direction proceedingdown through the top-sheet, thence into the layer of capillary channelfibers, and thence into whatever fluid storage core that may beprovided. The objective is to provide a gradient of capillary suctionbetween the topsheet and underlying layer or layers of the articlesherein, such that fluid is drawn in the "z" direction and away from thesurface of the article into its ultimate storage layer. Empirically,capillary suction is related to adhesion tension and inversely relatedto the size of the openings--i.e., in the typical case, the openings inthe topsheet will be larger than the intra-fiber capillary channels,which, in turn, will be larger than the inter-fiber capillary channelsin a fibrous storage core. The surface hydrophilicity of the componentsof each layer can theoretically affect the capillary suction gradient.

Simply stated, the capillary channel fibers used herein promote passageof fluids in the "z" direction of absorbent articles. Moreover, byemploying a layer of capillary channel fibers whose fibers arepositioned to lie substantially parallel to the machine direction, fluidflow in the machine direction is also promoted, which enhances theoverall useful absorbency of the article. However, by thus positioningthe capillary channel fibers, fluid flow in the cross direction iscontrolled, thereby minimizing, or even entirely avoiding, leakage offluid around the lateral edges of the article. Thus, unlike absorbentarticles of the prior art which move fluids in an undirected manner inthe x, y and z directions by means of fibrous batts which compriseinter-fiber capillary voids, the intra-fiber capillary channels of thefibers herein can be used to provide desirable fluid directionality.Moreover, since the capillary of the fibrous layer of the presentinvention resides in the fibers, themselves, rather than in inter-fiberspacings, capillarity is not lost when fiber-fiber spacings becomedisplaced. In addition, the capillary channel fiber layer of the presentinvention provides its fluid drawing and directing functions even whenthe layer is soft, fluffy and comfortable to the wearer, in contrast tocompact, dense and relatively stiff batt materials which function byinter-fiber capillary action. Thus, it will be appreciated that theabsorbent articles of this invention function in a substantiallydifferent way, using substantially different materials to providesubstantially different benefits than the various art-disclosedabsorbent structures which do not employ fibers having intra-fibercapillary channels.

It is to be understood that the manufacture of capillary channel fibersof the type employed herein forms no part of this invention. Attentionis drawn to EPO Application 391,814 (cited above) or to its co-pendingU.S. Continuation-In-Part Application entitled "FIBERS CAPABLE OFSPONTANEOUSLY TRANSPORTING FLUIDS", Ser. No. 07/736,267, filed Jul. 23,1991, Inventors Phillips, Jones, et al, Eastman Chemical Company, or tothe co-pending U.S. patent application entitled "OPEN CAPILLARY CHANNELSTRUCTURES, IMPROVED PROCESS FOR MAKING CAPILLARY CHANNEL STRUCTURES,AND EXTRUSION DIE FOR USE THEREIN", Ser. No. 07/482,446, filed Feb. 20,1990, Inventors Thompson and Krautter, all incorporated herein byreference, for further details regarding means for manufacturingcapillary channel fibers.

While a variety of capillary channel fibers can be used herein, thefollowing consideration of various points relating to the preferredcapillary channel fibers and their incorporation into the articles ofthis invention are included for the convenience of the formulator.

I. Fiber Structure and Surface Properties

The fibers used herein can be prepared from any convenient polymer whichis nonswelling when wet. Polymers such as polyethylene, polypropylene,polyesters (preferred), and the like, are useful herein, so long as theyare spinnable such that they can be formed with external capillarychannels, as noted hereinabove. Conveniently, the polymers aremelt-extrudable. Typically, the capillary channel fibers herein will beprepared from a synthetic polyethylene terephthalate polymer melt havingan inherent viscosity ("IV") of from about 0.6 to about 0.9. (IV is aterm of art and can be determined in well-known fashion. See, forexample, U.S. Pat. No. 4,829,761 at column 8.) The IV of a polymer meltbears some relationship to the ability of the polymer to retain theshape of the capillary channel walls, and is related to the averagemolecular weight of the polymers. For example, it is convenient toemploy a polyester having an inherent viscosity of about 0.7 herein, butit would be more preferred to employ a polymer having an inherentviscosity of about 0.9, since this would allow the walls of thecapillary channels to be thinner, yet sufficiently strong to avoidcollapse under in-use pressure. Preferred capillary channel fibersherein have a denier (denier per filament "dpf") of about 10, andcapillary channel fibers having such a fine denier, but whose walls arestable, can be achieved especially from polyester having an inherentviscosity of about 0.9. However, in commercial practice using such highIV polymers may require special processing equipment. As a quiteacceptable compromise, and in order to achieve capillary channel wallswithout in-use collapse, polyester/polymer having an inherent viscosityof about 0.7 can be employed at a denier per filament of about 22.However, it is to be understood that the denier of the fibers used iswithin the discretion of the formulator, and the denier per channel caneasily be in the range of 25.

The depth:width ratio of the capillary channels herein is preferablyabout 2.0, but processing restrictions, as noted above, as well as foreconomic reasons, a depth:width ratio of about 1.3 is typicallyemployed. Typical and readily producible capillary channel fibers whichare quite satisfactory for use herein thus have a depth-of-walls ofabout 48 microns and a width-between-walls of about 37 microns. Thewalls, themselves, are typically about 3-15 microns thick. Althoughvariations in these dimensions are acceptable, capillary channel fibersprepared from polyester and having these characteristics are quiteeffective for their intended purpose. Such fibers can be prepared usingconventional operating equipment and readily withstand pressures of thetype encountered in sanitary devices, especially sanitary napkins andpantiliners, without collapse or spreading of the capillary channelwalls to such an extent that their capillary function is lost.

The capillary channels can be of various shapes. Certain shapes canoffer particular advantages in particular product applications. Forexample,, "U-shaped", "H-shaped", " -shaped" and "V"-shaped capillarychannels may be used. The "H-shaped" fibers are one preferred shape.Furthermore, the basic shapes may be repeated (see Figures), or evenbranched, to produce fibers containing multiple channels, but it will beappreciated that when more than about three repeating shapes are used,some additional stiffness may be noted in the fibers. The multiple "U"fibers of FIG. 5 offer the additional advantages of having additionalcapillarity due to face-to-face contact and being easily curled.

While the polymers used to prepare the capillary channel fibers hereinare not, themselves, water-absorbent (nor are they absorbent to urine orblood-containing fluid such as menses), the fibers themselves are mostpreferably hydrophilic. Since most synthetic polymers are hydrophobic,the capillary channel fibers herein are surface-treated in order torender them hydrophilic. The surface treatment of polymeric fibersinvolves processes which are well-known in the extensive fiberliterature, and such processes can be used herein. In general, suchprocesses involve treating the surface of the fibers with a"hydrophilizing agent", especially a surfactant. (Hydrophilization,which results in wettability of the fibers by aqueous fluids, canroutinely be measured, for example, using contact angle measurements. Ingeneral, a contact angle less than 90° indicates a hydrophilic surface.A CAHN Surface Force Analyzer (SFA 222) can be used to measurehydrophilicity, as can a variety of other instruments known in the art.)Typical surfactants useful in such processes include various nonionicand anionic detersive surfactants of the general type known in thelaundry literature. Hydrophilizing agents include wetting agents such aspolyethylene glycol monolaurates (e.g., PEGOSPERSE 200ML, a polyethyleneglycol 200 monolaurate available from Lonza, Inc., Williamsport, Penna.,USA), and ethoxylated oleyl alcohols (e.g., VOLPO-3, available fromCroda, Inc., New York, N.Y., USA). Other types of hydrophilizing agentsand techniques can also be used, including those well known to thoseskilled in the fiber and textile arts for increasing wickingperformance, improving soil release properties, etc. Hydrophilizingagents can be added to the polymer at various stages prior to use,though preferably prior to drawing of the capillary channel fibers totheir final size. For example, the hydrophilizing agent can be added inadvance to the polymer prior to melting or blended into the polymersubsequent to melting. The additive hydrophilizing agent can also beapplied to the polymer subsequent to formation, e.g., subsequent to exitfrom an extrusion die in a melt, wet, or dry spinning process,preferably prior to drawing of the fiber to small diameter. Of course,since the articles herein are intended to come into contact withsensitive regions of the human body, it is preferred that surfactantsused to hydrophilize the surfaces of the capillary channel fibers benontoxic and nonirritating to human skin. Various surfactant treatmentsfor hydrophilizing the capillary channel fibers are described in theExamples hereinafter. Another method for hydrophilizing fibrous surfacesinvolves subjecting said surfaces to ionizing radiation, e.g., in aplasma, and such methods have the advantage that there is no surfactantresidue on the surface of the fibers. Whatever the means, the overallobjective is to secure capillary channel fibers for use herein which arespontaneously wettable by the fluids they are intended to transport.

II. Fiber Morphology

The capillary channel fibers herein have, as noted above and in thefigures, capillary channels on their outer surfaces. While the capillarychannel fibers can also have a hollow central core which would providesome additional capillarity, it is preferred that such hollow corefibers not be employed. In general, providing capillary channel fiberswith a central hollow core would require the fibers to be somewhatstiffer than desired in order that the core not collapse under pressure.A central core running through a capillary channel fiber would not beexpected to quickly pick up fluids, since the fluids would have to findtheir way to the end of a fiber before proceeding into the core itself.Moreover, a hollow core capillary channel fiber could not release itsload of fluid into an absorbent reservoir core without havingappropriate contact between the ends of the hollow core fiber and thereservoir core material. To summarize: capillary channel fibers havingexternal capillary channels offer substantial advantages in both pick-upand transfer of fluids, and the provision of a hollow core adds littlein the way of performance advantages, but can impact negatively on thecomfort level of an article made therewith in contact with the humanbody.

Moreover, the capillary channel fibers employed herein are preferablynot in a straight-line configuration; rather, they are either bent or,most preferably, are in a curled configuration. It is easy to appreciatethat capillary channel fibers that are nonlinear have, for a givennumber of fibers, a higher loft and increased resilience. By increasingthe loft of the individual fibers, the overall loft of pads madetherefrom is thicker and softer. This allows for the formation of lowdensity, high loft pads which, assuming that the individual fibersthemselves are not too thick or stiff (see denier, above), are extremelycomfortable, yet effective for transporting fluids.

However, the preferred nonlinear capillary channel fibers herein shouldnot be "kinked". As can also be readily appreciated, kinking a capillarychannel fiber can cause points of constriction of the capillary channelsat each kinking site. This, of course, would interfere with fluid flowdynamics along said capillary channel.

In addition to the foregoing, there is another substantial advantage toemploying nonlinear capillary channel fibers. As indicated in FIG. 12herein, it is highly preferred that small portions, or "tufts", of thecapillary channel fibers actually protrude into at least some of thetopsheet orifices of the articles herein. As can be imagined, theseprotrusions are easier to effect when a high loft capillary channel padis prepared using curled capillary channel fibers. Even by chance, thereis a greater likelihood that a number of ends and/or curls in thecapillary channel fibers will find their way into the orifices of thetopsheet material than if substantially linear capillary channels wereto be employed.

In a preferred mode, the capillary channel fibers herein are"substantially curled" (or otherwise gathered). As is known in the fiberart, fiber curling can be achieved by selectively heat quenching thefibers as they come from their forming die by heating one side of thefibers a bit more than the other side (or, conversely, by cooling oneside more quickly than the other). Alternatively, fibers made fromsynthetic polymers such as polyesters can be curled by stretching,followed by relaxation, or by passing the fiber under tension around asharp edge, followed by relaxation. Capillary channel fibers can also becurled by immersion in methanol. In a preferred mode, the fibers aresubstantially helical. Whatever means are used to crimp or otherwisegather the capillary channel fibers, they can, if desired, be carded toform an assembly of fibers.

The preferred amplitude of the curls is in the range of about 0.1 mm toabout 3 mm, and, typically, the frequency of the curls is from about 0.5per cm of fiber to about 5 per cm of fiber. Fibers with amplitudes ofabout 3 mm and a frequency of about 0.5 per cm exhibit good softnesseven in the higher denier ranged fibers having large capillary channels.Stated otherwise, an average capillary channel fiber having astraight-line length of about 2 cm is curled or gathered to provideoptimal fibers having a length of from about 0.5 cm to about 1.5 cm.

III. Multifiber Pads

Having thus considered the type of capillary channel fibers employedherein and their individual fiber morphology, the formulator of articlesprepared in the manner of this invention will be concerned in theformation of such fibers into absorbent articles. In general, theformulator will be laying-down a bundle of such fibers in the article.In one mode, the fibers can be blown onto, for example, an absorbentcore made from cellulosic fibers. In a more preferred mode, multiplecapillary channel fibers of the foregoing are formed into a batt or pad,said pad comprising a network of multiple capillary channel fibers. Suchmultifiber pads will typically have a caliper in the range from about0.1 in. (0.254 cm) to about 0.7 in. (1.78 cm), preferably from about 0.1in (0.254 cm) to about 0.4 in. (1.02 cm) for use in sanitary napkins;preferably from about 0.05 in. (0.127 cm) to about 0.15 in. (0.38 cm)for use in pantiliners; and preferably from about 0.1 in. (0.254 cm) toabout 0.5 in. (1.27 cm) for use in infant diapers or adult incontinencegarments. For use in disposable absorbent articles, such pads willtypically have from about 0.003 g to about 0.016 g of fiber per 1 cm²surface area, and will have from about 0.003 g to about 0.03 g capillarychannel fiber per 1 cm³ volume (measured in the uncompressed state). Theamounts of fiber per unit area and per unit volume for pantiliners,diapers and adult incontinence garments can be calculated based on thedifferences in caliper, noted hereinabove.

Preferably, the denier and strength of the capillary channel fibers willbe chosen such that the pad of fibers herein will have a ratio ofwet:dry caliper of at least about 80%, more preferably at least about90%. This ensures that the pad will retain its soft and form-fittingqualities even in use.

Stated otherwise, for a typical sanitary napkin, approximately 1.5 g ofcurled fibers of the type described herein will provide a rectangularpad having a surface area of about 160 cm² which is suitable for use aslayer (b), i.e., what might be termed a "secondary topsheet", underlyingthe initial fluid-receiving topsheet of the type disclosed hereinafter.

IV. Use of Multifiber Pads in Absorbent Articles

Having thus described the fibers, the fiber morphology and the inclusionof the fibers into a pad-like structure, the formulator of the absorbentarticles herein will now be concerned with the incorporation of suchpads into finished absorbent articles. It will be appreciated that thecapillary channel fiber pads prepared in the foregoing manner will,themselves, have some amount of holding capacity for fluids, such asmenstrual fluids, although this is not their primary function in thepresent articles. Accordingly, pads made in the foregoing manner can, ifdesired, comprise the entire absorbent core of, for example pantiliners.However, for most uses, the pad comprising the capillary channel fiberswill be used in conjunction with an absorbent core, said core serving asa reservoir for fluids which are transferred from the capillary channelfiber pad into said core. Indeed, most cores will comprise an air-laidfelt of cellulosic fibers, or mixtures of cellulosic fibers withabsorbent gelling materials. (It will be appreciated by the formulatorthat such cores are well-known for use in current, conventionaldisposable articles such as sanitary napkins, diapers, and the like.)Due to the extremely fine structure of the cellulosic fibers in suchabsorbent cores, the cores exhibit high suctional forces which tend todraw away fluids from the capillary channel fibers and into the core forultimate storage. This is precisely the intended effect. Thus, for asanitary napkin, typical cores which comprise from about 1 g to about 5g of multiple cellulosic fibers and, optionally, from about 0.5 g toabout 1.5 g of absorbent gelling material, are overlaid with a capillarychannel fiber pad prepared as described above. As fluid proceeds intothe article, it encounters the capillary channel fiber network, whichdistributes the fluid and then surrenders it to the underlying absorbentcore, thereby at least partially "renewing" the capillary channel fibernetwork for the next infusion of fluid. In a preferred mode, thecapillary channel fiber pad is used as a "secondary" topsheet under aporous (preferably formed-film) topsheet. Thus, the capillary channelfibers draw fluid through the topsheet, thereby leaving the topsheetwith a fresh, dry appearance and feel, then surrender the fluid to theunderlying absorbent core, and are thus able to continue the processuntil the core is saturated.

In a highly preferred mode, the pad of capillary channel fibers is keptin close contact with the overlying topsheet, either by adhesive bondingor by tensional forces, whereby the topsheet and capillary channel padremain in uniform, close contact. As noted above, contact between thetopsheet and the capillary channel fiber pad is, preferably, so closethat tufts of the capillary channel fibers extend into the orifices ofthe topsheet, itself. Likewise, in order to efficiently transfer fluidto the absorbent core, it is preferable that there be close contact(e.g., by adhesive or tensional forces, by providing a roughened surfaceof the absorbent core, or by needle-punching some of the capillarychannel fibers into the absorbent core) between the capillary channelpad and the underlying absorbent core. Thus, in a highly preferred modethere is an interconnecting network between topsheet, thence into thecapillary channel fiber pad, and thence into the underlying absorbentcore, whereby fluid efficiently proceeds through the topsheet, along andthrough the capillary channel pad, i.e., the "secondary topsheet", andinto the absorbent core. This interconnection is maintained even in theface of in-use stresses such as moisture, mechanical shear, andpressure-relaxation associated with physical movements of the wearer.

The individual elements used to prepare the articles of this inventionare described in detail, hereinafter.

TOPSHEET--The finished articles herein are provided with afluid-receiving topsheet. Such topsheets are made of materials which arepreferably hydrophobic, but fluid-permeable. Topsheet materials of thetype employed in the practice of this invention can be prepared bymethods well-described in the patent literature. For example, accordingto the process of U.S. Pat. No. 4,324,246, Mullane and Smith, Apr. 13,1982, a sample of thermoplastic material such as 0.0038 cm thickpolyethylene film is heated above its softening point. (The softeningpoint is the temperature at which the thermoplastic material can beformed or molded and is less than the melting point of the material.)The heated thermoplastic material in sheet form is then brought intocontact with a heated forming screen. The forming screen is preferablyan apertured wire mesh screen having the desired aperture size, patternand configuration. A vacuum is used to draw the heated film against theforming screen, thereby forming the film into the desired pattern andhaving the desired hole sizes. While the vacuum is still being appliedto the film, a jet of hot air is passed over the film. The hot air jetperforates the film in a pattern corresponding to the pattern and sizeof apertures in the forming screen.

Fluid-permeable topsheets prepared in the manner of the Mullane et alpatent are conveniently referred to as "formed films". The caliper ofsuch films is important since, if the caliper is too great, liquid mayaccumulate in the apertures and not readily pass there through. For themanufacture of absorbent articles such as diapers, catamenials,incontinence articles, and the like, the topsheets typically have acaliper of less than about 0.075 cm, or preferably less than about 0.064cm.

Another formed-film sheet material useful as the topsheet herein is theresilient, 3-dimensional web exhibiting a fiber-like appearance andtactile impression, comprising a fluid-impervious plastic material, withsaid web having a multiplicity of apertures, the apertures being definedby a multiplicity of intersecting fiber-like elements, all as disclosedin U.S. Pat. No. 4,342,314, Radel and Thompson, Aug. 3, 1982. The Radeland Thompson sheet materials can be prepared using hydrophobic plasticssuch as polyethylene, polypropylene, PVC, and the like, and arewell-known for use in absorbent products such as catamenials, and thelike.

Yet another type of formed-film sheet material useful herein isdescribed in U.S. Pat. No. 3,929,135, Thompson, Dec. 30, 1975, andconsists of hydrophobic polymer films having holes which are in the formof tapered capillaries. These "tapered capillary" topsheets are alsoknown for use in absorbent articles, including adult incontinencearticles. They may be prepared from various hydrophobic polymers, asmentioned hereinabove; typically, low density polyethylene havingthickness of from 0.0025 to 0.0051 cm is employed.

Reference to U.S. Pat. No. 3,929,135 can be made in order to furthervisualize tapered capillary topsheets. In use, the apices of thecapillaries in such tapered capillary topsheets are in contact with theunderlying absorbent core material . Generally, tapered capillaries arein the form of a frustrum of a conical surface, but it is to beunderstood that any generally tapered structure, such as a frustrum of apyramid or the like with a triangular, square, or polygonal base, iswithin the term "tapered capillary"; circular tapered capillaries,however, are used in this description for convenience. It is also to beunderstood that the tapered capillaries can be asymmetric (i.e., theangle of taper on one side can be different from that on another side)and that the angle of taper can change continuously (i.e., be curved)over the distance from base to apex. In the latter case, the angle oftaper is defined as the angle of the tangent to the side of thecapillary at its point of minimum apex opening dimension. The angle oftaper suitable for use in topsheets according to the practice of thisinvention is from about 10° to about 60°.

Base opening dimension of the capillaries is defined as the maximum openmeasurement in the plane of topsheet at said tapered capillary. Apexopening dimension is defined as the maximum open measurement in the apexof said tapered capillary, which apex is remote from the plane of thetopsheet. When the tapered capillary is in the form of a frustrum of aconical surface, the base and apex opening dimensions are, respectively,the base diameter and the apex diameter. Base diameter and apex diameterare hereinafter used interchangeably with, respectively, base openingdimension and apex opening dimension.

The tapered capillary apex diameter is a diameter which will allowliquid to readily pass from the surface of the topsheet to theUnderlying absorbent core. The apex diameter is from about 0.004 toabout 0.100 inch (0.010 to 0.254 centimeter), preferably from about0.005 to about 0.020 inch (0.013 to 0.051 centimeter).

The tapered capillary base diameter is selected to satisfy two criteria.The first of these is the subjective feel of the surface of the topsheetwhich contacts the skin of the user. It has been discovered thatpolyethylene can be made to exhibit pleasing, cloth-like, non-waxyattributes when the base diameter is within the range from about 0.006to about 0.250 inch (0.015 to 0.635 centimeter). Preferably, the basediameter should be within the range of from about 0.030 to about 0.060inch (0.076 to 0.152 centimeter). The second criterion is that thecapillary base diameter be small enough to allow an expected liquiddroplet to bridge across at least one capillary. This criterion issatisfied by the above dimensions for disposable diapers and sanitaryitems.

The height of the tapered capillary is defined as the distance betweenthe outermost surface of the topsheet (i.e., that surface which normallycontacts the skin of the user) and the apex of the tapered capillary.This height, of course, depends upon apex diameter, base diameter, andangle of taper which have been selected as hereinbefore described. Theheight of the tapered capillary should provide a structure with aminimum tendency to collapse in use. The characteristics of the materialof construction of the topsheet in large measure determine suitableranges for the height. When the topsheet is low density polyethylene offrom 0.001 to 0.002 inch (0.003 to 0.005 cm) thickness and apex diameterand base diameter are in the preferred range, and angle of taper α is inits critical range, the height of the tapered capillary can be fromabout 0.003 to about 0.159 inch (0.008 to 0.404 centimeter).

A state of relative dryness on the surface of the topsheet implies thatmost of the liquid which contacts the topsheet is transferred through itto the absorbent element. This in turn implies that each isolateddroplet of fluid in contact with the topsheet must be in contact withthe base diameter of a tapered capillary. This state of affairs can bestbe achieved if the land area (the area of the topsheet that existsbetween the bases of the tapered capillaries) is maintained at aminimum. The minimum limiting value is the case where conical taperedcapillaries or pyramidal tapered capillaries are provided in closepacked array (where the periphery of the base of each capillary is incontact on all sides with the periphery of the base of adjacentcapillaries). The preferred arrangement of minimum land area tends toinsure that an individual droplet will contact at least one taperedcapillary. A preferred arrangement in disposable diapers is where thetapered capillaries as hereinbefore described are in ordered arrangementwith from about 30 to about 1500 tapered capillaries per square inch oftopsheet (5 to 231 per square centimeter).

Tapered capillary sheets can be manufactured in any of several ways wellknown in the art. One particularly suitable method is to provide aheated mold with male elements of the shape and arrangement of thedesired tapered capillaries (hereinafter a pin mold). Each male elementis secured in such a fashion that its apex extends away from the base ofthe pin mold. A portion of sheet material is brought into contact withthe heated pin mold between the mold and a resilient backing plate.Pressure is applied to the combination of mold, sheet and resilient backplate and tapered capillaries are formed in the sheet to make thetapered capillary topsheet. An alternate way of constructing thetopsheet is to subject a portion of liquid-impervious material to vacuumforming over an appropriate mold. After forming tapered capillary sheetsin one of the aforementioned ways, it may be necessary to physicallyremove material from the apices of the capillaries so as to insure thatthe apex diameters are the desired value. Such removal of material canbe accomplished by, for example, subjecting the apices to controlledabrasion or by heating the formed topsheet so as to melt open theapices. See, also, U.S. Pat. No. 4,629,643, Curro and Linman, Dec. 16,1986, for a microapertured polymeric film with improved tactileimpression, which can also be used in the practice of this invention.

A highly-preferred fluid-permeable formed-film topsheet material whichcan be employed in the practice of this invention is disclosed in U.S.Pat. No. 4,463,045, Ahr et al, Jul. 31, 1984, and reference can be madeto that patent to further assist visualization of the Ahr et alstructures.

In general terms, the topsheets provided by U.S. Pat. No. 4,463,045 aredesigned not only to provide a desirable cloth-like tactile impression,but also to substantially eliminate surface gloss. Thus, topsheets madeof plastic do not have an undesirably shiny, "plasticky" appearance.

Such highly-preferred topsheet materials can be succinctly described asbeing a macroscopically expanded three-dimensional plastic "web" havingat least one visible surface which appears substantially non-glossy whenexposed to light, substantially all of said visible surface exhibiting aregularly spaced, microscopic pattern of discrete surface aberrations,each of said surface aberrations having its amplitude orientedperpendicular to the surface in which said surface aberrationoriginates, each of said surface aberrations having a maximum dimensionof less than about 6 mils, as measured in a plane oriented substantiallyperpendicular to its amplitude, whereby said surface aberrations are notdiscernible to the normal naked eye when the perpendicular distancebetween the viewer's eye and the plane of said web is at least about 12inches, each of said surface aberrations also being free of planar areaswhich are large enough to inscribe a 4 mil diameter circle and so spacedrelative to all adjacent surface aberrations that the maximum diameterof any circle which can be inscribed on any planar surface intermediatesaid surface aberration and said adjacent surface aberrations on anyportion of said visible surface is less than about 4 mils, whereby anylight incident upon any portion of said visible surface is diffuselyreflected into a multiplicity of directions by said surface aberrationsso that said visible surface appears substantially non-glossy.

The U.S. Pat. No. 4,463,045 topsheet materials can have at least aportion of said surface aberrations comprising protuberances projectinggenerally outwardly from the surface, and can have at least a portion ofsaid surface aberrations comprising depressions projecting generallyinwardly from the surface of said web.

The manufacture of these preferred topsheets can be achieved by use of aforming screen or structure, as generally noted hereinabove, whichprovides said surface aberrations by virtue of "knuckles" on the supportmember. (The preparation of such sheets is described in great detail inU.S. Pat. No. 4,463,045, and their method of preparation forms no partof this invention.) In general, the resulting surface aberrationscorrespond to the knuckles of a woven mesh support structure whichdirectly contacts the visible surface of said plastic sheet duringproduction thereof.

In a preferred manufacturing method, the woven mesh support structurewhich directly contacts the visible surface of said topsheet iscomprised of filaments having a diameter between about one and about twomils and a mesh count between about 160 filaments per lineal inch (2.54cms) by 160 filaments per lineal inch (2.54 cms) and about 400 filamentsper lineal inch (2.54 cms) by 400 filaments per lineal inch (2.54 cms).

Preferred topsheets herein are those wherein said surface aberrationshave an average amplitude of at least about 0.2 mils, more preferably atleast about 0.3 mils. Most preferably, topsheets having an amplitude ofeach of said surface aberrations, as measured perpendicular to thesurface in which said surface aberration originates, within the range ofabout ±20%, desirably ±10%, of the average value of the amplitude forall adjacent surface aberrations are used.

"One-way" formed-film topsheets whose backfaces are treated withhydrophilic latex are described in U.S. Pat. No. 4,735,843, Noda, Apr.5, 1988, and these can also be employed herein.

In addition to the sophisticated apertured materials mentionedhereinabove, the practice of the present invention may also beundertaken with hydrophobic sheet materials having simple holes punchedthere through.

It will be understood from the foregoing that the aforesaid, preferred,"sheet" or "film" materials used as the topsheet in the practice of thisinvention are substantially different from fibrous nonwoven materials,which are characterized by a large number of fibers which overlap eachother throughout the thickness of the material. Moreover, the topsheetmaterials used herein are made from materials (preferably, hydrophobicthermoplastic polymeric materials) which provide a clean-appearing,stain-resistant or "non-staining" surface, in use. Such topsheets (aswell as fibrous topsheets) can be rendered hydrophilic by spraying onsurfactants, e.g., PEGOSPERSE, in well-known fashion.

It will also be appreciated that fibrous, nonwoven topsheets made frommaterials such as polyethylene, polypropylene and blends are commonlyused in commercial sanitary napkins and pantiliners, and such fibroustopsheets can also be used herein.

Such fibrous, i.e., non-formed-film, topsheet materials which can beused herein include, for example, various nonabsorbent fibrous orfilamentous network sheets which are aqueous-fluid-permeable by virtueof a multiplicity of holes or channels passing therethrough. Such sheetmaterials can be prepared by methods well-described in the patentliterature. For example, according to the process of U.S. Pat. No.4,636,419, Madsen et al, Jan. 13, 1987, sheets comprising a network ofribboned filaments of two dissimilar chemical types, and with twodissimilar melting or softening points, are contacted and cooled toallow the formation of a network sheet characterized by said differenttransverse and longitudinal polymer materials. Such sheets can be usedin the practice of this invention.

Another sheet material useful herein is the formaminous net comprising areticular network of polymeric filaments, said net comprising two arraysof filaments oriented at a displacement angle of 20-90 degrees.Reference can be made to European Patent Application 0215417, filed Jun.9, 1986, Sneyd et al, to further assist visualization of this sheet. Theaforesaid sheet materials can be prepared using hydrophobic plasticssuch as polyethylene, polypropylene, PVC, and the like, and arewell-known for use in absorbent products such as catamenials, and thelike. Such sheet materials typically have a basis weight of 0.5-5.0ounces/yd² (0.0016 g/cm² -0.016 g/cm²), a caliper of 5-25 mils, an openarea of 30-80% and a mesh of 20-40. Conventional nonwoven topsheets canalso be employed.

Contact Between Topsheet and Capillary Channel Fibers--An importantconsideration in the manufacture of the articles herein is to ensureclose and sustained contact between the topsheet material and the layerof capillary channel fibers. Such close and sustained contact at theinterface of the fiber layer and the topsheet maximizes the fluidacceptance and fluid distribution properties of the finished articles.As noted hereinabove, one method of ensuring close contact is byadjusting the tensional forces between the topsheet and the layer ofcapillary channel fibers. While effective for its intended purpose,reliance on tensional forces can cause difficulties in manufacture, andcan even cause the article to assume a cup-type configuration.Ultrasonic bonding can also be used.

In a preferred mode, close contact between the topsheet and the layer ofcapillary channel fibers is achieved by means of adhesive bonding.However, even in this mode of operation some care is to be taken toachieve optimal results.

It will be appreciated that using excessive amounts of adhesive cancause the articles to undesirably stick to the body of the user.

It will also be appreciated that using excessive amounts of adhesivecould undesirably clog capillary channels in the fibers, therebydiminishing their effectiveness. Accordingly, "noninterfering" amountsof the adhesive are used. Such amounts can vary, depending on theadhesive chosen, the pattern in which it is laid-down, the width of thecapillary channels in the fibers, and the like. Controlling the area ofadhesive and the diameter of the adhesive lines in the spiral in themanner illustrated also serves to minimize the sticking of the articlesto the user's body.

The adhesive should be nonirritating to the skin and otherwisetoxicologically-acceptable for use in close contact with delicate bodytissues. The adhesive should maintain its bonding properties whenmoisture is not present, i.e., when the article is being manufactured,and, most preferably, when moisture is present, i.e., when the articleis being used.

The adhesive should bond both to the material used to manufacture thetopsheet and to the material used to manufacture the capillary channelfibers. If the topsheet or the fibers are surface-treated, e.g., in ahydrophilization process, the nature of the surface treatment will haveto be considered when selecting the adhesive.

Typical adhesives useful herein include materials selected from latexadhesives and hot melt adhesives. Fortunately, a great variety of suchadhesives are well-known in the art, and by giving appropriate attentionto the factors mentioned above, the manufacturer can select anappropriate adhesive for any set of circumstances. In order to sustaingood contact when the article is in use, i.e., becomes moistened by bodyfluids, it is preferred that the adhesive be insoluble in body fluids.

Having thus considered the general nature of the parameters which mustbe considered when bonding the topsheet to the layer of capillarychannel fibers, the following illustrates preferred materials andtechniques for use in the practice of this invention.

While the adhesive can be laid down in a random pattern, it is mostpreferred that a spiral, or multiple spiral, pattern, such as the oneillustrated in FIG. 10, be used. Alternatively, the spot pattern of FIG.11 can be used, but is less preferred.

In a preferred mode, the lines of adhesive are applied in the spiralpattern using a 0.2 mm nozzle, but application using nozzles at least aslarge as 0.6 mm is satisfactory.

The selection of adhesive can vary with the needs of the formulator, butthe following points are instructive. Experience has shown that, ingeneral, latex adhesives tend to be somewhat less satisfactory than hotmelt adhesives. Adhesives available from Findley Adhesives, Inc.,especially hot melt adhesive 4031, but also, almost uniquely, latex8085, are useful herein. (Note: Findley H-4031-01 is hydrophobic, whichmay account for its good performance properties. By contrast, latexH-8082-05 is hydrophilic and may undesirably separate when wetted underin-use conditions.) A variety of hydrophilic finishes can be present onthe capillary channel fibers, and the type of adhesive can varysomewhat, depending on the finish used, and its usage level. As noted,the objective is to ensure good contact between the topsheet and thelayer of capillary channel fibers at all times, thus maximizing fluidacceptance and partitioning properties. With the Eastman capillarychannel fibers such as SW194, Eastman's finish LK 5570 (49% PEG 400monolaurate/49% PEG 600 monolaurate/2% 4-cetyl-4-ethylmorpholiniumethosulfate [antistar]) works best with Findley adhesive 4031 at high,medium and low (0.78-0.87; 0.38-0.57; 0.28-0.33 wt. percent of fiber)finish levels. Typically, about 0.07 g, 0.08 g or 0.05 g, respectively,of Findley 4031 (depending on high, medium or low finish level) givesexcellent adhesion.

Other finishes herein include Eastman's LK 5483 (70% PM [PEG 600monolaurate, polyoxylaurate (13.64) monolaurate]/30% potassium laurylphosphate), Eastman's LK 5563 (45% PEG 400 monolaurate/45% PEG 600monolaurate/10% 4-cetyl-4-ethylmorpholinium ethosulfate) as well as thepolymer available as MILEASE T, which is well-known in the detergencyarts (see, for example, U.S. Pat. No. 4,132,680) as a fiber-coatingethylene terephthalate/polyethyleneglycol terephthalate soil releasepolymer, and which is available from ICI Americas.

As noted, the amounts of adhesive employed will vary, but typicallyrange from about 0.05 g for a 2 in.×5 in. spiral pattern to about 0.07 gfor a 2 in.×7 in. spiral pattern, using a hot melt adhesive. For a latexadhesive, from about 0.1 g to about 0.15 g for a 2 in.×5 in. patternwill suffice. For the spot pattern, about 0.05 g is used in an area ofca. 2 in.×5 in.

Close contact between the topsheet and the underlying layer of capillarychannel fibers can be further improved by applying pressure during thegluing process and/or by "combing" the uppermost capillary channelfibers in the layer to provide individual fiber protrusions which givebetter contact with the adhesive.

Irrespective of the bonding method employed, means for judging thecontact between the topsheet and the underlying layer of capillarychannel fibers relate to the speed with which fluid impinging on thetopsheet is drawn into the capillary channel fiber layer. Various meansfor judging transported fluid through the topsheet and into thecapillary channel fiber layer can be envisioned. However, a simple DropTest is conveniently employed. In this Test, sheep's blood or anydesired type of artificial menses is allowed to come to room temperaturewhile stirring at a gentle speed. With a catamenial pad layinghorizontally, the pad is visually sectioned into horizontal thirds.Using a dropper held approximately 1/2 in. above the pad, add 4individual drops of blood onto the topsheet of the top third of the padand add drops toward the middle of the pad at 1 in. intervals.Simultaneously, start the timer at the addition of the first drop ofblood or artificial menses. Record, in seconds, the time it takes eachdrop to penetrate the topsheet. Repeat the drop addition with 3 dropsadded to the middle third of the pad. Repeat the blood addition with 4individual drops being added to the bottom third of the pad. Average thereadings. Any descriptors selected by the formulator can be used todenote the speed of movement through the topsheet into the underlyinglayer of capillary channel fibers, and it will be appreciated that suchdescriptors will vary with the standards employed by the formulator. Ascore of Excellent can be attributed to fluid movement through thetopsheet and into the capillary channel layer in 1-10 seconds; a scoreof Good for fluid movement in a period of 10-15 seconds; a score of Fairfor movement in 15-20 seconds; and a score of Poor for periods of timegreater than 20 seconds.

In general, for sanitary napkins employing the formed-film topsheetaccording to U.S. Pat. No. 4,463,045, the layer of preferred capillarychannel fiber materials disclosed herein and the spiral gluing (hotmelt) pattern of FIG. 10, the movement of fluid through the topsheet andinto the capillary channel fiber layer is judged to be Excellent-to-Goodusing the above Drop Test.

Absorbent Core--Typically, finished absorbent articles will containsheets or batts of fibrous absorbent material such as cotton fluff,cellulose pulp, chemithermomechanical pulp, and the like, well-known incommercial practice. As is quite well-known from recent commercialpractice, cores which al so comprise absorbent gelling materials(sometimes referred to as "super-sorbers") are becoming broadly used inabsorbent articles. Especially preferred absorbent gelling materials arethe polyacrylates and acrylic acid grafted starch. The manufacture ofsuch wet-laid and air-laid absorbent cores is a routine matter. Variousfluid-absorbing sponges, peat moss, cotton, cloth, and the like,materials are also usable herein.

A particular type of absorbent core is preferred for use herein. In thistype of core, curled, twisted, preferably chemically stiffened andcrosslinked, cellulose fibers are refined to provide fibers which can beused in sheet form as the absorbent core. The preparation of suitablecurled, chemically stiffened cellulosic fibers from which one canprepare the refined, curled, chemically stiffened cellulosic fibers usedin the practice of this invention is described in great detail in U.S.Pat. Nos. 4,888,903; 4,822,543; 4,889,595; 4,889,597; 4,889,596; and4,898,642, incorporated herein by reference. Use of such fibers incombination with absorbent gelling materials, and means formanufacturing such combinations, are described in U.S. Pat. No.4,935,022. Such preparations typically involve the use of aldehydes,such as glutaraldehyde, as crosslinking agents. In addition,polycarboxylic acids can be used as crosslinking agents. (It will beappreciated that other means for preparing other crosslinked cellulosicfibers are also known, and such fibers may also be used herein, althoughthe fluid absorbency properties may be suboptimal as compared with theabove-mentioned fibers. Reference can be made to the various citationsin U.S. Pat. No. 4,898,642 and PCT U.S. No. 89/01581 for other fibertypes.) Once in hand, the curled cellulosic fibers are refined toprovide the fibers used to prepare the preferred absorbent cores used inthe practice of this invention.

Backsheet--The backsheet is conventional, and can comprise afluid-impermeable polymer sheet, for example polyethylene orpolypropylene, that is thin enough to be flexible. A polyethylene sheet0.001-0.5 mm thick is typical . Flushable or biodegradable backingsheets can also be used, e.g., with pantiliner devices herein.

Optional Retaining Means--The absorbent structures herein canoptionally, but preferably, be provided with means to hold them in placeon or near the user's body to allow the structures to perform theirintended function. For example, sanitary napkins can be provided withglue stripes facing outward on their back-sheet in well-known fashion.Various pins, clips and fasteners of well-known types can optionally beemployed.

The following examples further illustrate the practice of the invention,but are not intended to limit the absorbent articles encompassedtherein.

EXAMPLE I Thick Pad

A sanitary napkin article is hand-made using the following components.Reference is made to FIG. 13 for the assembly of the product.

The specifications of the finished product are as follows.

    ______________________________________                                                              Specifications                                          ______________________________________                                        Parameter                                                                     Pad weight (g)          9.82 ± 0.12                                        Core weight (g) laminate only                                                                         2.57 ± 0.04                                        Pad length (mm)         226 ± 1                                            Core length (mm)        197 ± 1                                            Pad width at center (mm)                                                                              81 ± 2                                             Core width at center (mm)                                                                             70 ± 0                                             Pad caliper (inches at 0.13 psi)                                                                      0.611 ± 0.02                                       Core caliper (inches at 0.13 psi)                                                                     0.058 ± 0.003                                      Seal length (mm)        8 ± 1                                              Components                                                                    Polyethylene ring rolled formed-film topsheet                                                         ca. 9" × 5"                                     (according to U.S. Pat. No. 4,463,045)                                        Capillary channel fibers SW194 (Eastman)                                                              1.5 g                                                 Capillary channel fibers SW173 (Eastman)                                                              0.5 g.                                                Findley extended adhesive backsheet                                                                   9" × 5"                                         (Formula #198-338)                                                            Creped BOUNTY paper towel                                                                             Shaped*                                               Panty fastening adhesive                                                                              Six 182" × 3/4"                                                         pieces; two                                                                   3/4" × 2.5"                                                             pieces                                                Release paper           As needed                                             Surfactant (PEGOSPERSE) 0.01 G                                                White poly for ends     4" × 0.75"                                      Absorbent gelling material (AGM) slit core                                                            70 mm × 193 mm                                  non-slit central area; total core wt.                                                                 with 23/4"                                            2.6 g; contains 0.7 g polyacrylate AGM                                                                non-slit                                                                      center area                                           Findley Adhesive-4031   0.05 g                                                ______________________________________                                         *See FIG. 13(38) for shape. The shape is designed to provide anatomical       fit.                                                                     

The SW194 fibers are of the H-shaped cross section having a denier ofapproximately 22 dpf, a channel width of about 37 microns and a channeldepth of about 48 microns. The SW173 fibers comprise a carded staplesliver which has been stuffer box crimped to 7.8 crimps per inch and arein the preferred H cross section, with a channel width of 38 microns anda channel depth of 19 microns. Capillary channel fibers SW194 are 6 in.long and capillary channel fibers SW173 are 2 in. long.

In the making procedure, the ring rolled topsheet is cut to the desiredsize, a template (2"×7" opening) is placed on the back side of thetopsheet and sprayed with the Findley 4031 adhesive. The adhesive isapplied in a spiral pattern (see FIG. 10). The layer of capillarychannel fibers SW194 is hand-pressed in the center of the glue sprayedarea. The fibers run parallel to the long axis of the article. Capillarychannel fibers SW173 are hand pressed as a swatch (with fibers parallelto the long axis of the article) in the center of the layer capillarychannel SW194 fibers. This provides a Pre-Assembly of the topsheet andcapillary channel fibers.

For convenience, the following procedure is carried out using a concaveforming die. The Findley adhesive backsheet (polyethylene backsheet withadhesive coating and release paper) is placed in the form. The AGMslitted core is placed over the backsheet, and the creped tissue(BOUNTY) is placed over the AGM core. The Pre-Assembly, prepared above,is placed over the creped tissue, as shown in FIG. 13. With thePre-Assembly over the creped tissue, the article's components are pulledsnugly over the edges of the form, but not so tightly that thecomponents begin to pull away from the form. Firm pressure is applied toadhere the edges with the adhesive on the backsheet. The article isremoved from the form and the ends are pressed in place using a roller.The release paper is peeled from the back of the backsheet. The endguard polyethylene strips are added and the strips of panty fasteningadhesive are placed on the article. The outer surface of the topsheet issprayed with 0.01 g of PEGOSPERSE surfactant.

EXAMPLE II Thin Pad

Reference is made to FIG. 13. The assembly of the thin pad isequivalent, except that CCF SW173 fibers are used in place of the layerof CCF SW194 fibers (36), and no swatch (37) of fibers is used.

Assembly of the product is as follows. Cut capillary channel fibers (CCFSW173) to 7 in. length; 0.75 g fibers used. Cut the ring-rolled topsheetto size. Place the template on the bottom side of the topsheet and applyFindley 4031 adhesive (spiral pattern). Hand-press CCF SW173 fibers inthe center of the glued area with the fibers running substantiallyparallel to the long axis of the topsheet. Lay the Findley backsheet onflat surface. Place the slitted AGM laminate core on the FindleyBacksheet. Center the S2 die shaped tissue over the laminate core.Center the topsheet/capillary channel fiber Pre-Assembly over the crepedtissue. Secure the Pre-Assembly and smooth at edges. Roll the edges toseal. Peel the release paper from the back of the pad. Tear and removein 2 or 3 pieces, then place the poly on the ends of the article. Placethe PFA on the pad. Spray the topsheet with PEGOSPERSE; 0.01 g.

The specifications of the finished product are as follows.

    ______________________________________                                                              Specifications                                          ______________________________________                                        Parameter                                                                     Pad weight (g)          8.50 ± 0.18                                        Core weight (g) laminate                                                                              2.54 ± 0.09                                        Pad length (mm)         232 ± 4                                            Core length (mm) laminate                                                                             201 ± 1                                            Pad width at center (mm)                                                                              85 ± 1                                             Core width at center (mm)                                                                             65 ± 1                                             Pad caliper (in. at 0.13 psi)                                                                         0.211 ± 0.005                                      Core caliper (in. at 0.13 psi)                                                                        0.074 ± 0.003                                      Components                                                                    Polyethylene formed-film topsheet (ring                                                               9" × 5"                                         rolled; per U.S. Pat. No. 4,463,045)                                          Capillary channel fibers SW173 (Eastman)                                                              0.75 g;                                                                       7" length                                             Findley extended adhesive backsheet                                                                   ˜9" × 5"                                  (Formula #198-338)                                                            Creped BOUNTY paper towel                                                                             Shaped*                                               PFA (panty fastening adhesive)                                                                        Six 3/4" × 3/4"                                                         pieces and two                                                                3/4" × 2.5"                                                             pieces                                                Release paper           As needed                                             PEGOSPERSE              0.01 g                                                White poly for ends     4" × 3/4"                                       AGM slit core non-slit center; total                                                                  65 mm × 193 mm                                  core weight 2.5 g; contains 0.7 g AGM                                                                 with 23/4"                                                                    non-slit center                                       Findley 4031 (adhesive) 0.05 g                                                ______________________________________                                         *As in Example I.                                                        

In the following Examples III and IV, the capillary channel fibers areused in absorbent articles whose absorbent cores comprise refined,curled cellulosic fibers. The manufacture of such refined absorbentfibers forms no part of this invention. Further details regarding theirmanufacture are described in the concurrently-filed U.S. patentapplication entitled "Absorbent Core for Use in Catamenial Products",Ser. No. 07/734,405, filed Jul. 23, 1991, Inventors Buenger, Horney andHammons, incorporated herein by reference. For the convenience of theformulator, the manufacture of such fibers, means for refining thefibers and means for forming said refined fibers into absorbent sheetsare described hereinafter.

Fiber Manufacture--The curled fibers prepared in the manner described inthe above-cited references comprise individualized curled cellulosicfibers which are preferably chemically stiffened by means of acrosslinking agent. As described in U.S. Pat. No. 4,898,642, such curledfibers have an average dry fiber twist count of at least about 4.5 twistnodes per millimeter an average wet fiber twist count of at least about3.0 twist nodes per millimeter and at least about 0.5 twist nodes permillimeter less than said dry fiber twist count; an average isopropylalcohol retention value of less than about 30%; and an average waterretention value of between about 28% and about 50%. Highly preferredfibers have an average dry fiber curl factor of at least about 0.30,more preferably at least about 0.50. It is to be understood that therefining process herein does not substantially affect the foregoingparameters, inasmuch as the process is carried out in such a manner thatthere is little or no defibrillation of the original curled and twistedfibers. Rather, the original fibers are, in general, reduced in length.0n average, the original curled fibers employed herein have lengthsranging approximately from about 1.6 mm to about 7 mm. After refining inthe manner disclosed herein, at least about 30% of the resulting fibers,preferably at least about 50%, more preferably about 90% of the refinedfibers have an average length which is from about 20% to about 40% ofthe length of the original, unrefined curled fibers. Stated otherwise,on average the unrefined fibers prepared by the above-referencedprocesses will have lengths in the range from about 1.6 mm to about 7mm, whereas, after refining, the lengths of the fibers will typically bemainly in the average range from about 0.25 mm to about 1.5 mm.

Fiber Refining--Once prepared by any of the aforementioned,art-disclosed processes, the curled cellulosic fibers are refined toprovide the fibers used in the practice of this invention.

In a typical process, an aqueous stock comprising about 3% by weight ofsaid fibers and 97% by weight water is passed through a Sprout-Waldron(now available as Sprout-Bauer) single disk refiner (available fromKoppers Company, Inc., Muncy, Pa., Model 105A-LAB) using a deknottingdisk of the 17804-A type. Importantly, it is the objective of therefining process herein to cut the twisted fibers without substantiallydefibrillating them.

The 3% aqueous stock solution is diluted to 0.5% consistency and flowsthrough the Sprout-Waldron refiner using a gap setting of from about 5mils to about 30 mils, preferably about 2.5 mils. (Note: TheSprout-Waldron is modified by removing the equalizing spring so that thegap setting remains constant throughout the flow of the fibrous stocksolution.) Typical flow rate is 9-10 gallons per minute and the refiningamperage is about 45 on a 25 hp. motor. (Use of the amperage term is ameasure of the mechanical energy imparted to the fibers during therefining.) A single pass of the fibers through the gap is employed.

In an alternate mode, the curled cellulosic fibers can be used incombination with crill, which is a highly refined southern softwoodkraft fiber having a Canadian standard freeness between about 50 toabout 100 ml. (TAPPI standard). Typically, the crill comprises up toabout 5%-10% by weight of the curled cellulosic fibers. Addition ofcrill can impart desirable strengthening properties to the final sheets,and also can serve as a diluent in the sheets, for reasons of economy.

Following the refining step, the 0.5% aqueous slurry of the refined,twisted fibers is further diluted to a slurry weight of from about0.1%-0.2% for use in the Sheet Formation operation, hereinafter.

Sheet Formation--In general terms, the formation of the above-preparedrefined, curled cellulosic fibers into sheets suitable for use as theabsorbent core in catamenials, and the like, employs a Fourdrinierpapermaking process with a standard fixed roof forming technique, andinvolving vertical transfer of the sheet across a through-air dryer.See, for example, U.S. Pat. No. 4,889,597. In the process, a breast rollis employed in the manner known in the art for preparing facial tissue,filter paper, and the like. However, unlike the manufacture of filterpaper, the sheet herein is dried without substantial pressure; rather,the through-air dryer system is employed.

In more detail, the above-described aqueous slurry comprising from about0.1% to about 0.2% by weight of the refined, twisted cellulosic fibersis introduced from the head box of the papermaking machine onto astandard forming wire. An objective is to avoid fiber flocculation,which would result in a nonuniform lay-down of fibers in the resultingsheet. The distance between the top of the head box and the forming wire(the "slice setting") is preferably set at about 90 mils to avoidflocculation. The dilution water can also be adjusted to avoidflocculation by settling. As noted, avoiding flocculation results insheets having a substantially uniform distribution of fibers.

Dewatering of the sheet is relatively rapid down to the 23% level. Avacuum box is employed to remove any excess water from the forming wire,after which the sheet is transferred to a drying fabric. Drying isaccomplished using a standard through-air dryer with an air temperatureof about 300° F. This results in a sheet having about 3%-4% by weightmoisture, which can requilibrate (depending on ambient humidity) to8%-10% moisture. It should be noted that the sheet is preferably notcompacted during drying, since this interferes with the absorbencycapacity. While the sheet formed in the foregoing manner is quiteabsorbent and suitable for use in many absorbent structures, it will beappreciated that such sheets may be somewhat stiffer than desired by theformulator of sanitary napkins and pantiliners. Using standardtechniques, the sheets can be calendered and/or passed through rollersin an "S" configuration to flex the sheet to the point that it becomessoft and pliable to the touch. This can be repeated, according to thedesires of the formulator.

It is to be understood that the sheets prepared in the foregoing mannerare highly absorbent and quite suitable for use in catamenial products.However, the sheets may lack strength for some purposes, especially whenmoistened and subjected to stresses, e.g., during wear by the user. Inorder to overcome this problem, it has been determined that a thin scrimof commercially available nonwoven, extremely porous, very low basisweight polypropylene, such as AMOCO D2 scrim, for example, can be laiddown on the forming wire of the Fourdrinier, after which the refined,curled fibers are formed into a sheet on top of the scrim. Duringformation of the sheet on such a scrim, small amounts of the fibers passthrough the scrim and attach the sheet to the scrim by a phenomenonreferred to in the art as "stapling". Preparing the sheet/scrim by thisprocess is preferred over the alternative process which would involveforming the sheet, placing the scrim on top of the sheet, and subjectingthe resulting scrim/sheet to vacuum. In this latter type of process ithas been noted that good "stapling" does not occur, and the scrim tendsto decouple from the sheet.

Fiber A--Fibers prepared according to the procedure of EXAMPLE I of U.S.Pat. No. 4,898,642 are refined in the foregoing manner. The slurry ofrefined fibers is formed into a tissue sheet having a Basis Weight(weight per 3,000 ft.²) of 35 pounds. The sheet can be used, forexample, in a tissue laminate having a central layer of polyacrylateabsorbent gelling material. Such laminates typically comprising about0.68 grams of the absorbent gelling material are useful as the absorbentcore in ultra-thin sanitary napkins of the type provided by the presentinvention.

Fiber B--Individualized, crosslinked fibers are made by a drycrosslinking process utilizing citric acid as the crosslinking agent.The procedure used to produce the citric acid crosslinked fibers is asfollows:

1. For each sample, 1735 g of once dried, southern softwood kraft (SSK)pulp is provided. The fibers have a moisture content of about 7%(equivalent to 93% consistency).

2. A slurry is formed by adding the fibers to an aqueous mediumcontaining about 2,942 g of citric acid and 410 ml of 50% sodiumhydroxide solution in 59,323 g H₂ O. The fibers are soaked in the slurryfor about 60 minutes. This step is also referred to as "steeping". Thesteep pH is about 3.0.

3. The fibers are then dewatered by centrifuging to a consistencyranging from about 40% to about 50%. The centrifuged slurry consistencyof this step combined with the carboxylic acid concentration in theslurry filtrate in step 2 set the amount of crosslinking agent presenton the fibers after centrifuging. In this example, about 5 weight % ofcitric acid, on a dry fiber cellulose anhydroglucose basis is present inthe fibers after the initial centrifuging. In practice, theconcentration of the crosslinking agent in the slurry filtrate iscalculated by assuming a targeted dewatering consistency and a desiredlevel of chemicals on the fibers.

4. Next, the dewatered fibers are defibrated using a Sprout-Waldron 12"disk refiner (model number 105-A) whose plates are set at a gap whichyields fibers substantially individualized but with a minimum amount offiber damage. As the individualized fibers exit the refiner, they areflash dried with hot air in two vertical tubes in order to provide fibertwist and curl. The fibers contain approximately 10% moisture uponexiting these tubes and are ready to be cured. If the moisture contentof the fibers is greater than about 10% upon exiting the flash dryingtubes, then the fibers are dried with ambient temperature air until themoisture content is about 10%.

5. The nearly dry fibers are then placed on trays and cured in anair-through drying oven for a length of time and at a temperature whichin practice depends on the amount of citric acid added, dryness of thefibers, etc. In this example, the samples are cured at a temperature ofabout 188° C. for a period of about 8 minutes. Crosslinking is completedduring the period in the oven.

6. The crosslinked, individualized fibers are placed on a mesh screenand rinsed with about 20° C. water, soaked at 1% for one (1) hour inabout 60° C. water, screened, rinsed with about 20° C. water for asecond time, centrifuged to about 60% fiber consistency, and dried to anequilibrium moisture content of about 8% with ambient temperature air.

The resulting individualized citric acid-crosslinked cellulosic fibersare refined in the above-described manner, and are formed into a sheeton an Amoco D2 scrim at a sheet/scrim Basis Weight of 150 pounds. Aftersoftening by passage over S-rolls, the sheet/scrim is suitable for usein the sanitary napkins of this invention.

Fiber C--Individualized crosslinked fibers are made by a drycrosslinking process utilizing 1,2,3,4 butane tetracarboxylic acid(BTCA) as the crosslinking agent. The individualized crosslinked fibersare produced in accordance with the hereinbefore described process ofExample II with the following modifications: The slurry in step 2 ofExample II contains 150 g of dry pulp, 1186 g of H₂ O, 64 g of BTCA and4 g of sodium hydroxide. In step 5, the fibers are cured at atemperature of about 165° C. for a period of about 60 minutes.

The resulting fibers are refined and formed into a sheet/scrim in themanner of Fiber B for use herein.

Fiber D--Individualized crosslinked fibers are made by a drycrosslinking process utilizing 1,2,3 propane tricarboxylic acid as thecrosslinking agent. The individualized crosslinked fibers are producedin accordance with the hereinbefore described process of Example II withthe following modifications: The slurry in step 2 of Example II contains150 g of pulp, 1187 g of water, 64 g of 1,2,3 propane tricarboxylicacid, and 3 g of sodium hydroxide. In step 5, the fibers are cured at atemperature of about 165° C. for a period of about 60 minutes.

The resulting fibers are refined and formed into a sheet/scrim in themanner of Fiber B for use herein.

Fiber E--Individualized crosslinked fibers are made by a drycrosslinking process utilizing oxydisuccinic acid as the crosslinkingagent. The individualized crosslinked fibers are produced in accordancewith the hereinbefore described process of Example II with the followingmodififications: The slurry in step 2 of Example II contains 140 g ofpulp, 985 g of water, 40 g of sodium salt of oxydisuccinic acid, and 10ml of 98% sulfuric acid.

The resulting fibers are refined and formed into a sheet in the mannerof Fiber A for use herein.

Fiber F--Individualized crosslinked fibers are made by a drycrosslinking process utilizing citric acid as the crosslinking agent andsodium sulfate as the catalyst. The individualized crosslinked fibersare produced in accordance with the hereinbefore described process ofExample II with the following modifications: The slurry as described instep 2 of Example II contains 200 g of pulp, 7050 g of H₂ O, 368 g ofsodium sulfate and 368 g of citric acid. The steep pH is about 2.0. Instep 5, the fibers are cured at a temperature of about 165° C. for aperiod of about 60 minutes.

The resulting fibers are refined as above and formed into a sheet/scrimhaving a Basis Weight of about 83 pounds. After softening by passageover S-rolls, the sheet is suitable for use in a pantiliner.

Fiber G--Individualized crosslinked fibers are made by a drycrosslinking process utilizing citric acid as the crosslinking agent andsodium hypophosphite as the catalyst. The individualized crosslinkedfibers are produced in accordance with the hereinbefore describedprocess of Example II with the following modifications: The slurry asdescribed in step 2 of Example II contains 326 g of pulp, 138 g ofsodium hypophosphite, 552 g of citric acid and 78 g of NAOH in 10,906 gof H₂ O. In step 5, the fibers are cured at a temperature of about 188°C. for a period of about 6 minutes.

The resulting fibers are refined and formed into a sheet/scrim having adensity of about 0.125 (at 0.1 psi pressure) and a capacity for sheep'sblood of about 8.0 grams of blood/gram of sheet. Such sheets are usefulat various Basis Weights in sanitary napkins and pantiliners.

In an alternate mode, the scrim used to support and strengthen theabsorbent core comprising the refined fibers can comprise capillarychannel fibers. Typically, such scrims comprise about 80% by weight ofthe capillary channel fibers and about 20% by weight of a fiber whosemelting point is below that of the capillary channel fibers. KODELfibers are suitable, for example. The scrim is prepared in standardfashion by heating to partially melt the lower-melting fibers, which, oncooling, bond the scrim together.

As noted, the layer of refined absorbent fibers is laid-down on thescrim. The resulting structure is then positioned such that the scrim isin fluid-communicating contact with the topsheet of the finishedabsorbent article.

EXAMPLE III

A lightweight pantiliner suitable for use between menstrual periodscomprises a one gram layer of SW173 capillary channel fibers overlayinga substantially rectangular pad having a surface area of about 117 cm²and containing the sheet/scrim comprising Fiber F as the absorbent core.The capillary channel fibers are laid down substantially parallel to themachine direction of the core. The sheet/scrim plus layer of capillarychannel fibers is interposed between the formed-film topsheet of U.S.Pat. No. 4,463,045 and a flexible polyethylene backsheet. Adhesivebonding of the capillary channel fibers to the topsheet is as disclosedhereinabove. The pantiliner functions to absorb vaginal dischargeswithout the need for absorbent gelling materials.

EXAMPLE IV

A catamenial product in the form of a sanitary napkin having two flapsextending outward from its absorbent core is prepared, per the design ofU.S. Pat. No. 4,687,478, Van Tilburg, Aug. 18, 1987. The absorbent corecomprises a sheet/scrim having a Basis Weight of about 150 pounds, perFiber G, herein. A 1.5 g layer of curled SW173 fibers overlays theabsorbent core, with the fibers parallel to the machine direction.Assembly follows the procedure of Example II, herein. The nonglossysheet of U.S. Pat. No. 4,463,045 is used as the topsheet.

EXAMPLE V

The sanitary napkin of Example IV is modified by needlepunching thelayer of capillary channel fibers to cause a substantial number of saidfibers to partially protrude downward into the absorbent core. Thisprovides additional fluid movement in the Z-direction, i.e., out of thelayer of capillary channel fibers and into the absorbent core.Alternatively, the upper layer of the absorbent core is combed orroughed such that fibers from the core extend upward into the layer ofcapillary channel fibers.

EXAMPLE VI

A thin pantiliner comprises a formed-film topsheet, a polyethylenebacksheet and a 2.0 g layer of curled capillary channel fibers SW173.The fibers have sufficient intra-fiber fluid capacity in their channelsto absorb a reasonable amount of vaginal discharge without the need forother absorbent materials.

EXAMPLE VII

The sanitary napkin of Example IV is modified by replacing itsformed-film topsheet with a fibrous topsheet according to U.S. Pat. No.4,636,419 or EPO 215417, respectively.

Having thus described the invention herein in great detail, someadditional points are included for consideration by the formulator. Itwill be appreciated that when capillary channel fibers are optionallyused as a scrim onto which is wet-laid an absorbent fibrous core, someof the surfactant on the surface of the capillary channel fibers can berinsed away. This can be readily replaced by application of additionalsurfactant, e.g., PEGOSPERSE.

It will be further appreciated that the in-use integrity of absorbentstructures comprising the refined, curled fibers disclosed above can befurther enhanced by various means. For example, ultrasonic or heatbonding can be used, especially in conjunction with the use of 10-15% byweight of thermoplastic fiber (e.g., KODEL 410 polyester) admixed withthe refined fibers. In yet another method, various spot-bonding meanscan be employed to affix the backsheet to the core, especially overthose areas to which the panty-fastening adhesive is applied.

Finally, it is to be appreciated that the preferred articles herein canemploy slitted or partially slitted absorbent cores, together withcurled capillary channel fibers and other extensible components which,together, provide a degree of extensibility (on the order of 15%-40%) tothe article. This extensibility provides better in-use fit, comfort anddecreased staining when the articles are affixed to the wearer'sundergarments.

In still another mode, the central portion of the layer of capillarychannel fibers can be gathered into a small "loop" or "tuft". This loopor tuft thus extends upward from the layer of capillary channel fibersto firmly contact the topsheet. Moreover, the loop or tuft is positionedcentrally in the overall article, such that it can provide rapidacquisition and transport of fluid into the remaining portion of thelayer of capillary channel fibers, and thence into the fluid storagelayer of the article. Advantageously, such "loop" or "tuft" not onlyconcentrates capillary channel fibers at the point where fluid impingesonto the article, but also orients the capillary channel fibers whichcomprise the loop or tuft substantially in the upward z-direction, thusenhancing fluid movement in the downward z-direction of the article. Thefollowing example illustrates an absorbent article having asubstantially central, z-directional tuft of capillary channel fibers.

EXAMPLE VIII

A layer of capillary channel fibers of the type disclosed herein (6-inchlength) is gathered in its center to provide a slightly raised oval"tuft" having the approximate dimensions: 2-3 inches (x-direction); 1.5inches (y-direction at widest point); and 5 mm-10 mm (z-direction). Thetufted bundle of fibers can be held in its tufted configuration by anyconvenient means. Typically, the tuft is passed through a confining slitin a sheet of paper or hydrophilic polymer. Using the proceduresdisclosed herein, the tufted bundle of fibers is assembled into anabsorbent article with the tuft residing approximately at the center ofthe overlying topsheet and with the tuft in close contact with thetopsheet, as explained hereinabove. In use as a sanitary napkin, thearticle is positioned (e.g., intralabially) to maximize fluid uptake bythe tuft. In an alternate mode, the ends of the looped fibers in thetuft are cut to provide a fleece-like, z-directional bundle ofopen-ended capillary channel fibers. In still another embodiment, thelayer of capillary channel fibers comprising the base of the tuft ispositioned wholly or partly within the wet-laid or dry-laid absorbentcore of the article, rather than atop the core. In this latterembodiment, a commercially-available layered laminate core comprisingtwo outer tissue layers with an intermediate layer of absorbent gellingmaterial (AGM) can be used. The capillary channels at the base of thetuft can be slipped into the internal, AGM-containing layer.

The capillary channel fibers can also be conveniently formed into astable sheet for ease-of-manufacture into absorbent articles by means ofvarious bonding processes. For example, about 20%-30% by weight ofpolyester thermoplastic fibers (e.g., KODEL 410) can be commingled withthe capillary channel fibers and the resulting fibrous sheet subjectedto direct thermal or through-air heating.

The refined curled cellulosic fibers can be conveniently formed into astable sheet for ease-of-manufacture into absorbent articles by means ofvarious bonding processes. For example, about 7%-15% by weight ofpolyester thermoplastic fibers (e.g., KODEL 410) can be commingled withthe refined curled cellulosic fibers and the resulting fibrous sheetsubjected to through-air heating or ultrasonic bonding.

Incorporation of the additional thermoplastic fibers into the capillarychannel fiber layer or into the absorbent core layer, or both, offersadvantages in addition to the sheet stability noted above. Inparticular, having the thermoplastic fibers present in the core, or inthe capillary channel fiber layer, or both, allows the manufacturer toprovide a seal at the periphery (at least in the crotch region) of, forexample, a sanitary napkin or panti-liner, said seal providing a meanswhereby fluid overflow around the edges of the article is impeded, orstopped altogether.

More particularly, an article of the foregoing type can be prepared bylaying-down a sheet of the refined curled cellulosic fibers containingthe thermoplastic fibers onto a standard plastic backing sheet. At aposition about 0.25 in. inboard from the outer edge of the sheet, asubstantially continuous ultrasonic bond approximately 0.125 in. wide isformed around the periphery of the core. This not only forms thefluid-impeding seal, but also bonds the core to the backsheet.

In an alternate mode, the thermoplastic topsheet, the core containingthe thermoplastic fibers and the backsheet can all be bonded together ator near the periphery by means of ultrasonic bonding. In still anothermode, the layer of capillary channel fibers containing the admixedthermoplastic fibers can likewise be bonded to the core (and also to thetopsheet, if desired). In still another mode, the presence ofthermoplastic fibers in the core and/or in the layer of capillary fibersallows for spot bonding at various points across the article, therebyproviding additional integrity when the article becomes wet.

While it will be appreciated by those familiar with the physics of fluidtransport that the articles herein conveniently make use of thedifferences in spacings between topsheet, capillary channel fibers andcore to establish a pressure gradient to draw fluids in the z-direction,other means can be employed to establish such z-direction fluid-flowgradient. For example, if the holes or spacings in the topsheet aresmaller than the width of the capillary channel fibers (and suchintra-fiber channel widths as wide as 90 microns may be useful fortransporting relatively thick fluids such as menses), then the desiredgradient can be established, for example, by selecting a topsheet whichis more hydrophobic than the capillary channel fibers.

What is a claimed is:
 1. A fluid receiving and fluid transportingstructure suitable for use in an absorbent article, comprising:(a) afluid permeable topsheet having a back face and a fluid-receiving frontface, said topsheet having multiple openings communicating between saidfront face and said back face for passage of fluid through saidtopsheet; and (b) a layer comprising multiple fibers having externalintrafiber capillary channels underlying the back face of said topsheetand in fluid-transporting contact therewith, said external intrafibercapillary channels being sized to draw fluid away from said openings insaid topsheet.
 2. A structure according to claim 1 wherein the contactbetween the topsheet and the layer of capillary channel fibers ismaintained by tensional forces between said topsheet and said layer. 3.A structure according to claim 1 wherein the contact between thetopsheet and the layer of capillary channel fibers is maintained bybonding means.
 4. A structure according to claim 1 wherein the capillarychannel fibers are substantially curled.
 5. A structure according toclaim 1 wherein the capillary channel fibers are substantially curledand portions of the capillary channel fibers partially protrude intosaid topsheet.
 6. An absorbent article comprising the structure of claim1, and additionally comprising:(C) a fluid-impermeable backsheetunderlying said layer of capillary channel fibers.
 7. An absorbentarticle comprising the structure of claim 6, additionally comprising:(d)an absorbent core positioned between said topsheet and said backsheet.8. A structure according to claim 1 wherein the capillary channel fibersare spontaneously wettable.
 9. A fluid receiving and fluid transportingstructure suitable for use in an absorbent article, said structurehaving a long axis and a short axis, said structure comprising:(a) afluid permeable topsheet having a back face and a fluid-receiving frontface, said topsheet having multiple openings communicating between saidfront face and said back face for passage of fluid through saidtopsheet; and (b) a layer comprising multiple substantially curledfibers having external intrafiber capillary channels sized to draw fluidaway from the openings in said topsheet, said layer underlying the backface of said topsheet and being in fluid-transporting contact therewith.10. A structure according to claim 9 wherein the capillary channelfibers are spontaneously wettable.
 11. A structure according to claim 9wherein the contact between the topsheet and the layer of capillarychannel fibers is maintained by tensional forces between said topsheetand said layer.
 12. A structure according to claim 9 wherein the contactbetween the topsheet and the layer of capillary channel fibers ismaintained by bonding means.
 13. A structure according to claim 9wherein portions of the capillary channel fibers partially protrude intosaid topsheet.
 14. An absorbent article comprising the structure ofclaim 9, additionally comprising:(c) a fluid-impermeable backsheetunderlying said layer of capillary channel fibers.
 15. An absorbentarticle comprising the structure of claim 14, additionallycomprising:(d) an absorbent core positioned between said topsheet andsaid backsheet.